Forget mousetraps: If you can build a better battery, the energy-hungry world will really beat a path to your door.

A New Hampshire startup spun out of Dartmouth’s engineering school thinks it can do that, using compressed air.

It’s called SustainX (despite how it seems, putting the letter “X” in a startup’s name is not mandatory; it’s just a quick way to turn an English word into a trademark-able name).

The firm launched in 2007, and in late August, it unveiled a unit that looks like an enormous engine but acts like a battery. It uses electricity to drive a crankshaft system that compresses air to 3,000 pounds per square inch, a hundred times the pressure in the average car tire.

It holds the air until the electricity is needed again, at which point it expands the air to drive a 1.5-megawatt generator – enough to power hundreds of homes for several hours.

Large-scale electricity storage is needed largely because solar and wind power is intermittent, as compared to always-on fossil fuel or nuclear power plants. Storing solar power for use at night or wind power for use in calm periods will be needed if we’re going to transition away from an electric grid that generates greenhouse gases.

Batteries, which tap into the flow of electrons between various liquids or solids, are expensive and difficult to scale up to sizes needed by power companies, so other technologies are being examined. They include the flywheel system pioneered by former Tyngsborough, Mass., firm Beacon Power (which has declared bankruptcy but isn’t dead); pumped water storage using dams; and even distributed systems that can tweak the temperature of people’s hot water tanks to turn them into a type of battery.

Compressed-air energy storage has been around for a while, but SustainX thinks its technology, especially the way it takes advantage of heat loss associated with compressing and expanding gasses, makes the process economical at large scale.